An investigation of anisotropy using AVAZ and rock physics modeling in the Woodford Shale, Anadarko Basin, OK


An investigation of anisotropy using AVAZ and rock physics modeling in the Woodford Shale, Anadarko Basin, OK

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dc.contributor.advisor Tatham, R. H. (Robert H.), 1943-
dc.creator Lamb, Alexander Peter Joseph 2012-07-20T16:46:18Z 2012-07-20T16:46:18Z 2012-05 2012-07-20 May 2012
dc.description.abstract The Woodford Shale formation is currently an important unconventional gas resource that extends across parts of the mid-continent of the United States. A resource shale acts as source, seal, and reservoir, and its characterization is vital to successful exploitation and production of hydrocarbons. This work is a surface seismic observation and investigation of the seismic anisotropy present in the Woodford Shale formation in the Anadarko Basin, Oklahoma. One of the main causes of anisotropy here is commonly believed to be vertical natural fractures (HTI) and horizontal alignment of clay minerals (VTI). Understanding the natural fracture orientation and density, as well as regional stress orientation, is important to the development of hydraulic fracturing programs in shales, such as the Woodford, producing natural gas. Dipole sonic log measurements in vertical boreholes suggest that the Woodford does possess vertical transverse isotropy (VTI), due possibly to horizontal layering or aligned clay minerals. Further, the borehole logs do not indicate horizontal transverse isotropy (HTI) associated with fracturing in the Woodford interval. An amplitude varying with angle and azimuth (AVAZ) analysis was applied to 3-D surface seismic data in the Anadarko Basin and shows the dipole sonic logs may not be completely characterizing the anisotropy observed in the Woodford. Once this apparent contradiction was discovered, additional work to characterize the fractures in the formation was undertaken. A petrophysical model based on the borehole data of the Woodford Shale was created, combining various techniques to simulate the rock properties and behavior. With a more complete rock physics model, a full stiffness tensor for the rock was obtained. From this model, synthetic seismic data were generated to compare to the field data. Furthermore, analytic equations were developed to relate crack density to AVAZ response. Currently, the application of this AVAZ method shows fracture orientation and relative variations in fracture density over the survey area. This work shows a direction for a quantified fracture density because the synthetic seismic data has a quantified fracture density at its basis. This allowed for a relationship to be established between explicit fracture parameters (such as fracture density) and AVAZ results and subsequently may be used to create regional descriptions of fracture and/or stress orientation and density.
dc.format.mimetype application/pdf
dc.language.iso eng
dc.subject Anisotropy
dc.subject Amplitude varying with azimuth
dc.subject Rock physics
dc.subject Resource shales
dc.subject Fracture orientation
dc.title An investigation of anisotropy using AVAZ and rock physics modeling in the Woodford Shale, Anadarko Basin, OK 2012-07-20T16:46:34Z
dc.identifier.slug 2152/ETD-UT-2012-05-5422
dc.contributor.committeeMember Spikes, Kyle T.
dc.contributor.committeeMember Sen, Mrinal K.
dc.description.department Geological Sciences
dc.type.genre thesis
dc.type.material text Geological Sciences Geological Sciences University of Texas at Austin Masters Master of Science in Geological Sciences

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